A known method for such a transmission of data is the Contention Resolution Diversity Slotted ALOHA (CRDSA) method. This method could for instance be used in the case of digital packetized uplink from many grounds stations towards a satellite. If we assume that there is no coordination between the users, i.e., the users may transmit their data packets on the same carrier frequency and in the same time instant and if we further assume that there is no Code Division Multiple Access (CDMA) it is obvious that packets sent by various users may collide on the communication medium, meaning that they will create interference among each other. The Slotted ALOHA method is a known protocol aiming to manage such uncoordinated multiple access schemes. In the Slotted ALOHA method the time access is partitioned in frames of duration Tf. Each frame is further partitioned in Ns slots of duration Ts=Tf/Ns. Each user must align his packet transmission to a slot, i.e., a synchronization with the frame structure must be kept by each user. Each user then transmits data independently with respect to the others and awaits for an acknowledgement form the gateway, which is the common access point. If no acknowledgement is received meaning that a collision has taken place on the communication medium, the user retransmits his packet with a random delay. This procedure is repeated until the packet transmission is successful. The concept of the Slotted ALOHA method is shown in FIGS. 1 and 2.
The throughput achieved by the Slotted ALOHA method is defined as T(G)=Ge−G. The peak throughput for the Slotted ALOHA method is achieved at G=1, for which T≃0.3679. This means that if G=1 the fraction of packets which will be transmitted successfully in a transmission attempt will be about 36%. G is defined as G=m/n, whereby m is the number of packet transmission attempts per frame and n is the number of slots per frame. The throughput which can be achieved with the Slotted ALOHA method as a function of the offered traffic G is shown in FIG. 3.